The present invention relates to a printing head, a head cartridge having the printing head, a printing apparatus using the printing head and a printing head substrate, and more particularly, to data transmission/reception between a printing head and a printing apparatus using the printing head.
Electrothermal transducers (heaters) of a printing head mounted on a printing apparatus according to a conventional ink-jet method and a driver which drives the electrothermal transducers in accordance with an input image signal are formed on one substrate by using a semiconductor process technique, as disclosed in Japanese Published Unexamined Patent Application No. Hei 5-185594. Further, it has been proposed to form a device to detect condition of the substrate such as temperature of the substrate, distribution of resistance values and variation of characteristic of the driver, on the same substrate.
FIG. 8 is a block diagram conceptually showing a method for detecting the condition of a substrate in a conventional ink-jet printing head.
In FIG. 8, reference numeral 101 denotes a semiconductor substrate or a base plate (hereinbelow referred to as xe2x80x9csubstratexe2x80x9d) constructing a printing head; 102, a heater array having a plurality of electrothermal transducers (heaters) to generate thermal energy necessary for discharging ink; 103, a heater of the heater array 102; 104, a power transistor block to drive the heater by supplying a desired current to the heater; 105, a logic circuit comprising a latch circuit, a shift register and the like, for ON/OFF controlling the respective heaters in accordance with data transfer from the outside of the printing head; 106, a power source line for applying a predetermined voltage to the heaters, thus supplying the current to the heaters; 107, a GND line which the current that flowed through the heaters and the power transistor enters; and 108 and 109, a GND terminal and a power source terminal for leading the power source line to the outside of the printing head.
Further, numeral 410 denotes a temperature detection device for detecting the temperature of the substrate 101; 411, wiring for transmitting a signal from the temperature detection device 410; 412, a terminal for leading the signal from the temperature detection device 410 to the outside of the printing head; 420, a resistor for monitoring a resistance value of the electrothermal transducers formed on the substrate; 421, wiring for applying a voltage to the resistor 420 to measure a resistance value of the resistor; 422, a terminal for leading the wiring 421 to the outside of the printing head; 430, a signal processor block for processing an output from the temperature detection device and that from the resistance value monitor resistor; 413 and 423, wiring for connecting the temperature detection device 410 and the resistor 420 with the signal processor block 430; 440, a judgment circuit block for receiving an output from the signal processor block 430 to detect the condition of the substrate and feeding back appropriate control in accordance with the detected condition to the substrate; 450, wiring connecting the signal processor block 430 with the judgment circuit block 440; and 460, wiring connecting the judgment circuit block 440 with the logic circuit 105 in the substrate.
Next, the conception of control in accordance with substrate temperature detection and a detected temperature in the conventional printing head will be described with reference to FIG. 8.
The power transistor supplies a current for generating thermal energy necessary for ink discharge to the heater array 102. The timing of current supply is as follows. The judgment circuit block 440 determines an optimum driving method and the like corresponding to the condition of the substrate at that time, then a control signal according to the determined driving method is sent to the logic circuit 105, and the logic circuit 105 supplies the control signal to a control terminal of the power transistor.
At this time, the amount and period of heat generation by the heater are determined by the timing of current that flows through the heater, and ink corresponding to the amount is discharged for the period. However, as the heat generation energy by the heater is supplied not only to the ink but also to the substrate 101, the temperature of the substrate 101 rises. Accordingly, ink discharge cannot be performed on a constant condition. That is, it is difficult to maintain the same ink discharge condition in a wide temperature range at constant drive timing. For this reason, there is a need to drive the heaters while detecting the substrate temperature and selecting an optimum ink discharge condition.
Preferably, the device to monitor a temperature change in the substrate has a known temperature characteristic. For example, a P-n junction diode is employed and its forward voltage-current characteristic or the like is utilized. Stable ink discharge can be maintained in a wide temperature range by providing the diode on the substrate, detecting the change of characteristic of the device at predetermined intervals from an external position, and supplying optimum drive timing corresponding to each detected result.
That is, in FIG. 8, a predetermined voltage is applied to the power source terminal 109 in advance, then if a timing pulse based on print information and driving condition is inputted from the logic circuit 105 into the power transistor block 104, a corresponding heater 103 in the heater array 102 is driven, and a nozzle at a specific position corresponding to the driven heater discharges ink.
At this time, if heat generation operation with respect to the heater is continuously repeated, the temperature of the substrate rises corresponding to the heat generation operation. The temperature detection device 410 sends an output signal corresponding to the temperature of the substrate, via the substrate internal wiring 411 and the terminal 412 and the substrate external wiring 413, to the signal processor block 430 on the printing apparatus side. Generally, the output from the temperature detection device 410 is an analog signal. The signal processor block 430 amplifies the analog signal, converts the output into a digital value, and sends the digital vale via the wiring 450 to the judgment circuit block 440.
The judgment circuit block 440 detects the temperature rise of the substrate 101 by the digital value, and sends a driving signal indicative of an optimum driving condition at the temperature via the wiring 460 to the logic circuit 105. The logic circuit 105 supplies a timing pulse corresponding to the substrate temperature to the power transistor, and as a result, the heater is driven and ink is discharged.
In this manner, even if the substrate temperature changes, a stable ink discharge condition can be maintained by detecting the substrate temperature at predetermined intervals.
Next, the conception of monitoring of resistance value of the electrothermal transducer (heater) formed on the substrate in the conventional printing head and control in accordance with the result of monitoring will be described.
In the ink-jet printing head, upon printing, heat generated by the heater 103 boils ink, and the ink is discharged by a pressure of bubble generated by boiling. The quantity of heat (Q) generated at this time is expressed by Q=I2R with the current (I) which flows the heater and the resistance value (R) of the heater. According to the relation between the quantity of heat (Q) and the resistance value (R), the quantity of heat (Q) changes based on the resistance value (R) of the heater itself, and the formation of bubble changes in correspondence with the change of the quantity of heat (Q).
When the printing head is exchanged for a new one, the quantity of heat (Q) depends on the resistance value of the heater of the new printing head. However, as the heater resistance value varies by each heater, if the heaters are always driven on the same driving condition, the quantity of heat changes, and uniform printing cannot be performed. Generally, if the heaters comprise a metal or metal alloy thin film resistor formed by a semiconductor process, the manufacture-caused variation is about xc2x120%.
For this reason, there is a need to maintain stable ink discharge with respect to the variation of resistance value by detecting the resistance values of the respective heaters of the printing head and supplying optimum timing for each heater from an external device.
That is, in FIG. 8, a device of the resistor 420 used for monitoring the heater resistance value is formed with the same material as that of the actually-heat generating heater 103 and by the same process as that of the heater. The resistance value of the heater is read by the signal processor block 430 via the internal wiring 421 and the terminal 422 of the substrate and the external wiring 423.
The output from the resistor 420 to the outside of the printing head is an analog signal. The signal processor block 430 amplifies the analog signal, then converts the output into a digital value, and sends the digital value via the wiring 450 to the judgment circuit block 440. The judgment circuit block 440 detects the heater resistance value by the digital value, and feeds back a driving signal indicative of optimum driving condition corresponding to the resistance value via the wiring 460 to the logic circuit 105.
Thus, even if the heaters have different resistance values, a stable ink discharge condition can be maintained by performing the above control when the printing head is exchanged for new one, or when the power of the printer main body is turned on.
Further, it has been proposed to transmit printing head ID (identification) information for drive control change, rank information for determination of printing parameters, and the like, as well as the temperature of the substrate as described above, from the printing head to the apparatus main body.
However, in the above conventional art, the information indicative of detected substrate temperature and information indicative of monitored heater resistance value are outputted as analog signals from the substrate to an external device. Therefore, the above information is easily influenced by power source noise which occurs upon flow of a large current in synchronization with ink-discharge heat pulse, GND noise, coupling noise which enters the wiring toward the outside of the substrate, radiation noise and the like. Accordingly, the information cannot be precisely read
Further, providing a noise eliminator, a device or the like to reduce the above noise increases the number of parts constituting the printing head and the space of substrate, thus increases costs. Further, to use the analog signals as control signals, it is necessary to convert the analog signals into digital values by an A/D converter then send the digital values to the judgment circuit. In this case, the A/D converter which must be provided at an external position of the printing head will make the configuration of the entire system complicated, and increases the costs.
Generally, signal transmission/reception between the printing head and the printing apparatus main body is performed by using input/output pads (PAD). However, the number of pads increases for transmission/reception of printing head identification information, rank information and the like as well as the above temperature information. This construction has the following drawbacks.
(1) As the number of pads increases, the area of substrate of the printing head increases, which increases the apparatus in size and costs.
(2) As the number of pointing wires for electrically connecting the pads to external contacts increases, the increase in printing head manufacturing steps leads to increase in the costs.
(3) The increase in the number of control signal lines disturbs cost reduction with simplification of substrate.
Especially, in a case where printing head identification information and/or rank information are transmitted to the apparatus main body side, the number of wires from the printing head to the main substrate of the apparatus main body increase in proportion to the amount of information, which increases contact portions (pads) and both substrate areas, and increases the costs.
Further, as the information which varies with time such as temperature information must be transmitted periodically even during a printing operation, the information is transmitted by using it""s own transfer clock rather than using the clock for the printing data. For this purpose, the wiring for the clock is added to the wiring. At this time, as the transfer clock signal becomes a noise source with a print data clock, a wiring route for the clock must be considered for avoid generation of noise. Further, to reduce influence by generated noise, a special circuit and/or part may be necessary.
Further, generally, the temperature of the printing head is detected by using a comparator. However, as it takes time to change a reference voltage and start the comparator, if print data transfer from the printing apparatus is made at a high speed, the transfer of temperature data cannot be made on time.
Especially, if the speed of print data transfer from the printing apparatus is reduced to the same speed as the speed of temperature data transfer, such low speed cannot meet a recent requirement for high-speed printing. Further, although the reference voltage change and the operation of the comparator can be made at a high speed, as electric consumption at analog circuits to perform these operations increases, the electric consumption in printing stand-by condition (i.e., the condition where the temperature detection is not performed) becomes larger than that in digital circuits for receiving and storing print data.
To address this problem, it has been considered to control power supply to the analog circuits from the outside of the printing head, however, the voltage drop at a control circuit for ON/OFF controlling the power supply influences the precision of temperature detection, further, the number of signal lines connecting the printing head to the external devices increases.
Accordingly, an object of the present invention is to provide a printing head which has an increased noise-resistant characteristic in an output from a sensor device provided for monitoring various condition of the printing head and obtains more precise sensor output, further has a reduced number of circuits and/or devices for noise elimination, thus attaining cost reduction, and a printing apparatus using the printing head.
According to the present invention, the above object is attained by providing a printing head according to a first aspect of the present invention where an electrothermal transducer for generating thermal energy used for discharging ink and a driver for driving the electrothermal transducer are provided on a substrate, comprising: a sensor which detects the condition of the substrate and outputs an analog signal; and an A/D converter which converts the analog signal from the sensor into a digital value, wherein the sensor and the A/D converter are provided on the substrate.
The driver may include: a power transistor which drives the electrothermal transducer; a shift register in which print data to drive the power transistor is temporarily stored; and a latch circuit which latches the print data stored in the shift register.
Further, the condition of the substrate includes at least one of temperature of the substrate, a resistance value of the electrothermal transducer and an ON resistance value of the power transistor.
Preferably, the sensor has a p-n junction diode having a known temperature characteristic for detecting the temperature of the substrate, a resistor of the same material as that of the electrothermal transducer, formed by the same process as that of the electrothermal transducer, for detecting the resistance value of the electrothermal transducer, and a transistor of the same conduction type of that of the power transistor, formed by the same process as that of the power transistor, for detecting the ON resistance value of the power transistor.
Further, it is preferable to provide a nonvolatile memory in which digital information indicative of the resistance value of the electrothermal transducer, the ON resistance value of the power transistor and the like is stored, such as an EPROM, an EEPROM or a fuse ROM which does not change with time, on the substrate. Preferably, the digital information indicative of the resistance value of the electrothermal transducer and the digital information indicative of the ON resistance value of the power transistor, stored in the nonvolatile memory, were obtained by factory-shipment measurement.
In the printing head according to the first aspect of the present invention having the above construction, the output from the device for detecting the conditions of the printing head is digitized on the substrate, and the digital information is outputted to the outside.
Further, the above object is attained by a printing apparatus which performs printing by using the printing head having the above construction, and having control means for performing drive control on the printing head.
Further, the above object is attained by providing a printing head substrate having an electrothermal transducer for generating thermal energy used for discharging ink and a driver for driving the electrothermal transducer, comprising: a sensor which detects the condition of the substrate and outputs an analog signal; and an A/D converter which converts the analog signal from the sensor into a digital value, wherein the sensor and the A/D converter are provided on the substrate.
According to the first aspect of the present invention, as the output from the device for detecting the conditions of the printing head is digitized on the substrate, and the digital information is outputted to the outside. For example, the information indicative of the temperature of the substrate, the resistance value of the electrothermal transducer, the ON resistance of the power transistor which drives the electrothermal transducer and the like is sent to an external printing apparatus as digital values. Accordingly, the digital values are not easily influenced by power source noise, GND noise, coupling noise, radiation noise and the like when the digital values pass through wirings and the like. Thus, the precision in the signal reading is improved, and precise printing head drive control can be performed without influence by noise.
Further, an A/D converter or the like which conventionally converts analog signal from the printing head into digital information can be omitted from the main body of the printing apparatus.
Further, as noise elimination means to reduce the power source noise and GND noise is omitted, the entire construction and space of the apparatus can be simplified.
Further, another object of the present invention is to provide a printing head which can reduce the apparatus in size and production cost of the apparatus by reducing the number of pads on the substrate of the printing head, and a printing apparatus using the printing head.
The above object is attained by providing, printing head according to a second aspect of the present invention, which performs printing by discharging ink in accordance with an ink-jet method, comprising: a memory for storing printing characteristics of a plurality of printing elements for discharging ink; a converter which converts an analog signal into digital signal and outputs the digital signal; and a driver which drives the plurality of printing elements in accordance with an input print signal, wherein the printing characteristics are read from the memory by using a clock signal and a latch signal for inputting the print signal, and wherein the digital signal is outputted from the converter by using the clock signal.
Preferably, each of the plurality of printing elements driven by the driver comprises: a heater; a switch which ON/OFF controls energization of the heater; and a discharge nozzle which discharges ink heated by heat generation by the heater.
Preferably, the driver has a shift register and a latch circuit. Further, the driver has: a first input pad which inputs a heat pulse signal with respect to the heater; a second input pad which inputs a print signal into the shift register; a third input pad which inputs the clock signal; and a fourth input pad which inputs a latch signal with respect to the latch circuit.
On the other hand, it is preferable that the memory includes: a plurality of ROMs; and a plurality of shift registers one-to-one corresponding to the plurality of ROMs, wherein a read signal is outputted from the plurality of shift registers to the plurality of ROMs, in accordance with the clock signal inputted from the third input pad, such that information stored in the plurality of ROMs are sequentially outputted.
Further, the converter inputs the read signal outputted from the plurality of shift registers and generates a threshold signal for analog/digital conversion. Further, it may be arranged such that the converter has a reduction circuit which reduces a frequency of the read signal outputted from the plurality of shift registers. The converter performs analog/digital conversion on the analog signal, in accordance with the frequency reduced by the reduction circuit.
Note that as the analog signal, an output from a temperature sensor which measures an internal temperature of the printing head can be used.
Further, according to the second aspect of the present invention, as reading of printing characteristics of the plurality of printing elements to discharge ink stored in the memory and conversion of analog signal into digital data can be performed by utilizing the clock signal and the latch signal for the print signal, the number of signals inputted into the printing head can be reduced, and the number of pads necessary for inputting the signals can be reduced.
By this arrangement, the size of the substrate of the printing head can be reduced, and the size reduction and the reduction of the number of pads reduces circuit production cost.
Further, the reduction of the number of signals inputted into the printing head reduces the number of signal lines, which suppresses occurrence of noise, further prevents erroneous operation due to noise with the suppression of noise occurrence, thus maintains high-reliable operation of the printing head.
Still another object of the present invention is to provide a printing head which prevents increase in the number of wires and the substrate area even if the amount of information transmitted from the printing head to the apparatus main body increases, and which suppresses production cost, and a printing apparatus using the printing head.
The above object is attained by providing a printing head according to a third aspect of the present invention, which performs printing in accordance with an input print signal, comprising: a nonvolatile memory for storing information on the condition of the printing head; and output means for outputting the information stored in the memory in a serial format to outside of the printing head, by utilizing a clock signal and a latch signal used for inputting the print signal, within a period in which the print signal is inputted.
In this case, it may be arranged such that the printing head further comprises conversion means for converting the information on the condition of the printing head into digital data, and outputting the digital data in the serial format to outside of the printing head, by utilizing the clock signal and the latch signal used for inputting the print signal, within the period in which the print signal is inputted.
Preferably, identification information of the printing head is stored in the nonvolatile memory. The nonvolatile memory includes at least one of an EPROM, an EEPROM and a fuse ROM.
Preferably, the output means outputs the information stored in the memory bit by bit, in synchronization with the clock signal.
According to the third aspect of the present invention, the information from the printing head can be sequentially outputted as a digital signal in synchronization with a clock used for print data transfer. By this arrangement, it is not necessary to provide a D/A converter on the apparatus main body side, and further, even if the amount of information to be transmitted increases, the number of signal lines does not increase. Accordingly, the devices do not increase in size and costs. Further, the number of clock signals as noise sources is only one, which does not much influence the environment. Further, stable head information transfer can be performed by digital transfer.
Further, at the same time of printing, information acquisition can be made without limiting the period of data transfer, accordingly, high-speed printing and fine control utilizing the information transferred from the printing head can be performed.
Yet another object of the present invention is to provide a printing head which detects temperature information and transmit the information while allowing high-speed print data transfer, and a printing apparatus using the printing head.
The above object is attained by a printing head according to a fourth aspect of the present invention, which outputs temperature information in accordance with input of print data, comprising: a shift register which inputs print data in accordance with a first-frequency clock; a heater which is energized and generates heat in accordance with the print data; a temperature detector which detects an internal temperature of the printing head; and a frequency divider which divides a frequency of the first-frequency clock and generates a second-frequency clock, wherein the temperature detector outputs a signal indicative of a detected temperature in accordance with the second-frequency clock.
Preferably, the temperature detector has: a temperature sensor; a reference voltage generator which generates a reference voltage; a switching circuit which changes the reference voltage in accordance with the second-frequency clock; and a comparator which compares an output voltage from the temperature sensor with the reference voltage from the switching circuit, and outputs the result of comparison as a signal indicative of the detected temperature.
Preferably, the frequency divider divides the frequency of the first-frequency clock by two.
Preferably, the printing head further comprises a latch circuit which latches print data stored in the shift register.
According to the fourth aspect of the present invention, the print data is inputted into the shift register in accordance with the first-frequency clock, while the first-frequency clock is divided by two so as to generate the second-frequency clock. The temperature detector to detects the internal temperature of the printing head outputs the signal indicative of the detected temperature in accordance with the second-frequency clock. Even if the print data input speed for printing operation increases, the speed of output of the signal indicative of the detected temperature is low, the operation speed of the temperature detector may be low.
By this arrangement, it is not necessary to increase the operation speed of the temperature detector, and the cost necessary for the increase in the operation speed can be saved. Accordingly, cost-saving printing head temperature control and high-speed print data transfer can be attained.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.